The pasteurization of eggs calls for a never-ending balancing of factors. For example, the United States Department of Agriculture ("U.S.D.A.") has set minimum criteria for the pasteurization of liquid whole egg and other egg products. See, U.S. Dept. of Agriculture, Egg Pasteurization Manual ARS 74-48, February 1969. Pasteurized liquid whole egg which has been processed in accordance with these minimum standards does not pose a danger to the consumer from, for example, salmonella, and the like, poisoning and retains substantially all of its baking functionality. That is, the thus treated egg product is able to be used in the most rigorous of baking applications. However, the refrigerated shelf life of these eggs is relatively short, on the order of 7 to 14 days, and the total concentration of secondary bacteria remains high.
If higher temperature pasteurization is used, such as for example, 152.degree. F. for the same 3.5 minutes, the refrigerated shelf-life of the resulting liquid whole egg can be dramatically increased to 4-10 weeks, or even longer. However, the resulting liquid whole egg product has lost significant baking functionality. In fact, at this temperature and time, the egg product may begin to coagulate and may thus lose its liquid quality.
Obviously, the development of a liquid egg product and, in particular, a liquid whole egg product which has both an extended refrigerated shelf life and retained baking functionality would be highly desirable. More importantly, however, the development of an economically efficient process which utilizes cost effective apparatus for the production of such an egg product has long been sought. Yet the solution to providing an egg product satisfying both of these requirements, and a cost effective manner of making these liquid eggs have eluded the industry.
Koonz et al., U.S. Pat. No. 2,565,311 relates to a method of egg pasteurization which involves the step of shelling whole eggs, hashing or homogenizing the liquid egg, flash heating the liquid egg to a temperature of between about 138.degree. to 150.degree. F., and then pasteurizing the liquid egg at a temperature of between about 125.degree. to 145.degree. F. This is followed by the steps of chilling the liquid egg to between 40.degree. and 55.degree. F. and then freezing the pasteurized liquid egg. Koonz et al. therefore represents a single step pasteurization method wherein shelled eggs are flash heated to raise their temperature followed by a pasteurization step and subsequent cooling and freezing.
Jones et al., U. S. Pat. No. 3,113,872 relates to a method of treating shelled eggs which includes first subjecting the shelled egg to a first heating step where the egg is heated to about 143.degree. F. by the heated metal surface of a conventional plate heat exchanger for about 30 seconds. The heated egg is next transferred to a vacuum chamber where volatile esters are removed. During this treatment, the heat is maintained at a temperature of not less than 140.degree. F. for a period of about 3.0 minutes. The egg is then infused with steam to raise its temperature to between about 155.degree. F. and 165.degree. F., and preferably to about 158.degree. F.
According to Jones et al., it is important that the liquid egg must remain at an elevated temperature throughout the process and especially just prior to steam infusion so that the egg does not have a great chilling effect on the steam. Furthermore, it is important that the final heating step be conducted in the absence of heated metallic surfaces. According to Jones et al. it is only by the use of a final heating step which does not include contact with a heated surface that the temperature of the egg can be elevated to a high enough temperature.
None of these methods, nor other methods of which the inventors are aware, have been capable of conveniently and efficiently producing liquid whole egg or other liquid egg products which have both extended refrigerated shelf life and retained baking functionality. The present invention allows for the realization of just such a liquid egg product in an economically feasible way.